Conventionally, there has been known an optically anisotropic film containing an organic dye having a sulfonic acid group.
This optically anisotropic film is obtained, for example, by coating a solution containing the organic dye and water on a base material, followed by drying.
The optically anisotropic film containing an organic dye having a sulfonic acid group is inferior in water resistant. Therefore, it is known that this film is subjected to a water resistant treatment.
Patent Document 1 discloses that a film containing an organic dye having a sulfonic acid group is made water resistant by bringing the film into contact with a solution containing a metal salt such as a barium salt.
Patent Document 2 discloses that a film containing an organic dye having an anionic group is made water resistant by bringing the film into contact with an insolubilizing liquid containing a cationic compound with a value obtained by dividing the molar volume by the valence of 30 cm3/mol or more and having two or more valences.
However, in these methods, it is difficult to control the reaction rate in the water resistant treatment. Therefore, due to the fact that the reaction rate is too high, a defect that a crack is generated in the film, or in the case where the optically anisotropic film is formed on a base material, the film is separated from the base material, is generated.    Patent document 1: JP-A-11-21538    Patent document 2: JP-A-2009-199075